Make sure you have the right kind of Airport card. If it is an extreme, it will not work in the older towers. Also make sure you seat it properly. But yeah, sounds like a bad card if it's an actual older Airport card...

There are cheaper options; the DWL-122 dongle is great for laptops, and has been much better supported in the past year (it used to cause kernel panics. but the newest driver was released in November or December (I think) and is very stable, at least in 10.2 and 10.3). There are also several companies that make PCI wireless for your tower and PCMCI for your laptop which will work with mac. All of them are way cheaper than a classic airport card.

Or you could go to your local univerisity or college computer store and pick up a brand new airport card for under $100 , most schools will sell you non systems and software stuff with out a student card.
Last year my school was selling airport cards for $69 canadian , I bought 3 and sold them on ebay for $135USD each plus shipping...

The original airport cards aren't for sale anywhere anymore, to my knowledge, other than secondhand and rarity places. I could be wrong, though. EDIT: which, apparently, I am. Can you still get them for $69 Canadian? I may have to take a trip to Vancouver, as I have three machines that could use them...

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